1. Field of the Invention
The present invention relates to a method and an apparatus for recording/reproducing information with respect to an optical recording medium by irradiating an optical recording medium, which has a thin film including a recording layer on a substrate, with a high-energy beam such as a laser beam. In particular, the present invention relates to a method enabling information recorded on an optical recording medium to be reproduced in a shorter period of time.
2. Description of the Related Art
Recently, optical recording media that allow information to be recorded/reproduced/deleted, and optical recording apparatuses that record/reproduce information with respect to the optical recording media have been commercialized. Furthermore, rewritable optical recording media with high density that allow animation of high quality to be recorded/reproduced, and optical recording apparatuses therefor have been studied and developed extensively. As a rewritable optical recording medium, a phase-change type optical recording medium is known, which has a chalcogenide thin film of Ge—Sb—Te, In—Sb—Te, or the like on a disk-shaped substrate with uneven tracks. A magneto-optical recording medium that has a metal thin film of Fe—Tb—Co or the like as a recording layer also is known.
In a phase-change type optical recording medium, for example, a recording thin film layer made of a phase-change material as described above is irradiated with a focused laser beam, whereby an irradiated portion is heated locally to a predetermined temperature. The irradiated portion shifts to a crystalline state when it reaches a crystallization temperature or higher, and it shifts to an amorphous state when it reaches a temperature exceeding a melting point, followed by rapid cooling. Either the amorphous state or the crystalline state is defined as a recording state or a deleting state (non-recording state), and an amorphous mark is formed on a medium with a pattern corresponding to an information signal, whereby recording is conducted. Furthermore, the change in these states is reversible, so that information is recorded or deleted repeatedly. The crystalline state and the amorphous state have different optical characteristics. Therefore, a signal can be reproduced by optically detecting a change in reflectance or in transmittance, utilizing the difference in characteristics.
In a magneto-optical recording medium, for example, a magneto-optical recording thin film is irradiated with a focused laser beam, so as to be heated locally to a predetermined temperature. A magnetic field is added to the film concurrently with heating, and a magnetization direction of the film is inverted in accordance with information, whereby information is recorded or rewritten repeatedly.
Hereinafter, a conventional method for recording/reproducing information with respect to an optical recording medium with high density will be described.
When an optical recording medium is loaded in an optical recording apparatus, the optical recording medium starts rotating. Then, the optical recording apparatus sets the laser power at reproduction power, and sets a servo condition for a laser beam to scan a track under a focus condition and a tracking condition for recording/reproducing information. In order to record information on the optical recording medium with optimum laser power, the power of a semiconductor laser is increased or decreased previously to extract the optimum write power (power learning). Furthermore, according to a method for correcting a recording pulse train appropriately in accordance with an information pattern to be recorded as suggested by JP 7-129959 A, an optimum recording pulse condition is extracted (recording pulse learning). When a series of operations is completed, the optical recording apparatus becomes capable of recording/reproducing information with respect to the optical recording medium, and information can be read from and recorded on the optical recording medium in accordance with a command from a personal computer.
However, in the case where the optical recording medium is loaded in the optical recording apparatus, and information is read from the optical recording medium as described above, the information starts being read only after a series of learning steps such as power learning, recording pulse learning, and servo learning is conducted and a host computer is informed that the optical recording apparatus becomes available. Thus, a lot of time is required for a series of learning steps. These learning steps are likely to take a longer period of time in an optical recording medium ready for high-density recording. In some cases, for example, tens of seconds are required for extracting an optimum recording condition by learning. Thus, the conventional method has a problem in that a user's waiting time (from loading an optical recording medium to reproducing data therefrom) becomes long.
Furthermore, during this waiting time, the user is just on standby without taking advantage of it.